1. Field of the Invention
The present invention relates to an apparatus for formatting an information storage medium and more particularly relates to an apparatus for setting a certification format.
2. Description of the Related Art
Recently, various removable information storage media with big storage capacities and drives for performing read and write operations on such media have become immensely popular.
Examples of known removable information storage media with big storage capacities include optical disk media such as DVDs (Digital Versatile Discs) and BDs (Blu-ray Discs). An optical disk drive writes data on an optical disk medium using a laser beam. Specifically, a red laser beam is used for DVDs, while a blue laser beam, having a shorter wavelength than the red laser beam, is used for BDs, thereby making the storage density and storage capacity of BDs higher and greater than those of DVDs.
FIG. 1 illustrates an exemplary layout of areas on an optical disk medium. The disklike optical disk medium 1 has a spiral track 2, along which a great many blocks 3 are arranged.
As far as BDs are concerned, the track 2 should have a width (which is also called a “track pitch”) of 0.32 μm according to the standard. Blocks 3 are not only units of error correction but also the smallest units of read/write operations. Each block 3 is supposed to be one ECC (with a size of 32 KB) on DVDs and one cluster (with a size of 64 KB) on BDs. If these units are represented on the basis of a sector, which is the smallest data unit for optical disk media and has a size of 2 KB, one ECC is equal to 16 sectors and one cluster is equal to 32 sectors.
For BDs, a logical sector called “AUN” (where one logical sector is equal to two sectors and has a size of 4 KB) is sometimes used.
On BDs, data in each block 3 is classifiable into user data to be stored in a data block and addresses and other flag information to be stored in a flag block. FIG. 2 shows the data format of a block 3 on a BD.
As shown in FIG. 2, a parity, which is an error correction code, is added to each of the user data in the data block and the flag information in the flag block, thereby forming an LDC cluster and a BIS cluster, respectively. Then, the data in these two clusters are interleaved together to form an ECC cluster. In each block (or cluster) 3 of a BD, stored is data in this data format called “ECC cluster”. The data in the BIS cluster is smaller in size the data in the LDC cluster. However, the parity data added to the BIS cluster is comparable to that added to the LDC cluster. That is why the data in the BIS cluster realizes extremely high error correction ability and is much more likely to be read correctly than the data block corresponding to the LDC cluster.
In the following description, “cluster” will refer to such a block 3 on BDs. It should be noted, however, that the cluster does not have to be equivalent to the block.
FIG. 3 shows the structure of a recordable optical disk medium.
The optical disk medium 1 includes a lead-in area 4, a data area 5 and a lead-out area 6.
The data area 5 includes a user data area 14 and two spare areas 15a and 15b. 
The user data area 14 is an area on which the user can write any type of information he or she likes, including real time data such as music and video and computer data such as documents and databases.
The spare areas 15a and 15b are alternative areas to store data in place of some block 3 in the user data area 14. For example, if a defective block has been detected in the user data area 14, one of these spare areas 15a and 15b is used as an alternative area to replace that block. In the example shown in FIG. 3, the spare areas 15a and 15b are arranged inside and outside of the data area 5 so as to be adjacent to the lead-in area 4 and the lead-out area 6, respectively.
The lead-in area 4 is located inside of the data area 5, while the lead-out area 6 is located outside of the data area 5. These areas 4 and 5 not only store management information about the optical disk medium 1 but also prevent the optical pickup (not shown) from making an overrun.
The lead-in area 4 includes first and second defect management areas 10 and 11 (which will be referred to herein as “1st DMA” and “2nd DMA”, respectively). Each of the 1st and 2nd DMAs stores disk management information such as information about the data structure and defects of the optical disk medium 1.
The lead-out area 6 includes third and fourth defect management areas 12 and 13 (which will be referred to herein as “3rd DMA” and “4th DMA”, respectively). Each of the 3rd and 4th DMAs stores disk management information such as information about the data structure and defects of the optical disk medium 1.
It should be noted that the DMA normally stands for a defect management area. However, as the DMA may store not only defect management information but also various other types of information about a disk (which is called “disk management information”), the DMA may sometimes stand for a disk management area in a broader sense.
The 1st through 4th DMAs are arranged in their own areas on the optical disk medium 1 and store quite the same information, which is done to prepare for a situation where any of the 1st through 4th DMAs has gone defective. That is to say, even if information can no longer be retrieved from one of these four DMAs properly, the defect management information can still be acquired as long as there is at least one DMA from which information can be retrieved properly.
Each of the 1st through 4th DMAs has a disk definition structure (which will be abbreviated herein as “DDS”) 20 and a defect list (which will be abbreviated herein as “DFL”) 21.
The DFL 21 includes defect entries 23 that store information about alternation processing such as the locations of the defective block and its replacement block and a defect list header 22 including the identifier of the DFL 21, information about the number of times of update, and information about the total number of defect entries 23.
Next, an address showing the location of the block 3 will be described. The “address” may be a physical address (or physical sector number, which will be abbreviated herein as “PSN”), which is a piece of information about the physical location of the block 3 on the storage layer of the optical disk medium 1, or a logical address (or logical sector number, which will be abbreviated herein as “LSN”) to be virtually assigned consecutively to the data area 5 that can be accessed by a host device (i.e., a logical space). These addresses are usually assigned on a sector-by-sector basis. Or a predetermined number of addresses may be assigned to each block 3.
A PSN on a BD-RE, which is a rewritable BD, may be either an address called “ADIP” represented by the wobbled side surface of the track 2 or an address called “AUN” to be assigned to the data stored in the block 3. On the other hand, LSNs are a series of address information that is virtually assigned consecutively to the data area 5 and that starts with zero. The LSNs are usually addresses that are supposed to be assigned sequentially to all blocks 3 and that start with zero assigned to the first block in the user data area 14. If any of the blocks 3 in the user data area 14 has been subjected to the alternation processing, however, the LSN that would have been assigned to the original block will be assigned to the replacement block in one of the spare areas 15a and 15b. 
The physical sector numbers (PSNs) are addresses that are assigned in the ascending order along the track path on the disk. In a BD-RE with two storage layers (which will be referred to herein as L0 and L1 layers, respectively), an addressing method called “opposite path” is adopted. That is why physical addresses are assigned to the L0 layer in the ascending order from the inner area of the disk toward the outer area thereof. On the other hand, physical addresses are assigned to the L1 layer in the ascending order from the outer area of the disk toward the inner area thereof.
Next, the certification processing will be described. Rewritable optical disk media such as DVD-RAMs and BD-REs are normally subjected to so-called “certification” processing to determine in advance whether the given block 3 in the data area 5 is a normal block or a defective block. Specifically, the certification processing is a testing method in which arbitrary data is written on a block 3 and that data is read from the block 3 for verification purposes to determine whether the written data is identical with the read data. If the answer is YES, that block 3 is certified as a normal block. On the other hand, if writing or verification has failed or if it has been determined that the written data disagrees with the read data, then that block 3 is detected as a defective block that cannot be used normally and information about the location of that defective block is added to the defect list 21 (see Patent Document No. 1, for example). Also, if the disk has the spare areas 15a and 15b for alternation purposes, a block 3 in the spare area 15a or 15b may be assigned to the block that has turned out to be defective as a result of the certification processing (see Patent Document No. 2, for example).
There are several different types of certification processing. In one type of certification processing, the entire storage area on the disk is subjected to certification. In another type of certification processing, only a particular area on the disk is subjected to certification. As for a BD-RE, for example, two modes called “full certification” (which will also be referred to herein as “full certify”) and “quick certification” (which will also be referred to herein as “quick certify”) are defined as parts of formatting processing to be carried out to initialize the disk management information such as the DDS 20 or the DFL 21 (see Non-Patent Document No. 1). These types of processing are included in so-called “formatting processing” to be carried out to initialize the data area 5, i.e., to get the data area 5 ready to write user data on. In the area that has been subjected to any of these processes, there is no valid user data.
Specifically, the “full certify” is a mode in which all blocks 3 included in the data area 5 are subjected to certification.
On the other hand, the “quick certify” is a mode in which only the defective blocks on the defect list 21 are subjected to certification in the data area 5. This mode of processing is carried out to get minimum required blocks 3 tested more quickly than the “full certify” processing.
Next, the defect entries 23 of a BD-RE will be described.
FIG. 4 shows the makeup and types of the defect entries 23 of a BD-RE.
FIG. 4A and FIG. 4B show the makeup of the defect entries 23. Each defect entry is eight bytes (=64 bits) of information including an entry attribute 30 representing the category of the defective block, defect location information 31 such as the top physical address of the defective block that should be replaced, sub-information 32 that is additional information for the entry attribute 30 and replacement's location information 33 such as the top physical address of the replacement block to replace the defective block.
FIG. 4B shows the types of the defect entries 23 of a BD-RE, i.e., the types of the entry attributes 30. There are five entry attributes 30 including RAD, NRD, SPR, PBA and UNUSE.
Specifically, the RAD attribute represents the attribute of a defect in a single block, its defect location information 31 includes the top physical address of the defective block, and its replacement's location information 33 includes the top physical address of the replacement block in the spare area 15. RAD includes RAD0 indicating that the replacement block has actually been written as a replacement for the defective block and RAD1 indicating that the replacement block has been assigned to the defective block but actually has been written as a replacement yet (i.e., the block identified by the replacement's location information 33 has not been used yet). The RAD0 attribute may be expressed as “0000” and the RAD1 attribute may be expressed as “1000” according to the binary notation.
The RAD0 and RAD1 attributes are different in that when a data read request has been submitted, data is read from either the replacement block (according to RAD0 attribute) or the original (i.e., defective) block (according to RAD1 attribute). If a data write request has been submitted, then the replacement block is accessed no matter whether the attribute is RAD0 or RAD1.
It should be noted that a piece of information representing a “discard” state may be set as a binary number “1000”, for example, for the sub-attribute 32 of RAD0. The “discard” state indicates that a portion of the data that should have been written in the original block is actually written in the replacement block as will be described in further detail later.
The NRD attribute represents a single defective block that has not been replaced yet, and the defect location information 31 includes only the top physical address of the defective block. The NRD attribute may be represented as a binary number “0001”, for example.
The SPR attribute designates a block that can be used as a replacement block in the spare area 15, and its replacement's location information 33 includes the top physical address of the replacement block. The SPR attribute may be represented as a binary number “0010”, for example.
It should be noted that a piece of information representing a “RDE” state may be set as a binary number “0100”, for example, for the sub-attribute 32 of the SPR attribute. The “RDE” state indicates that the replacement block identified by the replacement's location information 33 has once been detected as defective and could still be defective.
The PBA attribute represents an area including at least one block that could be defective. Its defect location information 31 includes the top physical address of that area and its replacement's location information 33 includes the number of continuous blocks. The PBA attribute may be represented as a binary number “0100”, for example.
It should be noted that a piece of information representing a “RDE” state may be set as a binary number “0100”, for example, for the sub-attribute 32 of the PBA attribute. The “RDE” state indicates that the area identified by the defect location information 31 and the replacement's location information 33 has once been detected as defective and could still be defective.
The UNUSE attribute designates a single defective block in the spare area 15a or 15b, and its replacement's location information 33 includes the top physical address of the defective block. The UNUSE attribute may be represented as a binary number “0111”, for example.
In the defect list 21 (see FIG. 3), stored are the defect entries 23 that have been sorted in the ascending order by the eight-byte values thereof. Speaking more exactly, the defect entries 23 are stored in the defect list 21 after having been sorted in the ascending order by their 63-bit values except their most significant bits. RAD0 and RAD1 are treated as the same attribute. That is to say, the defect entries 23 have been grouped according to their entry attributes and then sorted in the ascending order.
Hereinafter, the “discard” state mentioned above will be described in further detail. Data is basically read and written from/on a rewritable optical disk medium 1 on a block-by-by basis. As for a BD-RE, for example, reading and writing is performed on a cluster (=64 KB) basis. However, the host PC may request to write data, of which the size is even short of the block unit. In order to satisfy such a request, the drive for reading and writing data from/on the optical disk medium 1 has a so-called “read-modify-write” function (which will be abbreviated herein as an “RMW function”).
FIG. 5 shows the procedure of RMW processing, in which a BD-RE is supposed to be used as a storage medium. It should be noted that by adding h to the end of a numeral, a hexadecimal number is expressed.
Hereinafter, it will be described with reference to FIG. 5 what processing should be carried out in response to a request of writing data, which has a top physical address 110h and of which the size is 8h (corresponding to four logical sectors), on a cluster, which has a top physical address 100h and of which the size is 16 logical sectors (corresponding to 20h when represented as a difference in address). That is to say, the size of the data to be written is smaller than that of the cluster unit.
In Step (1), data is read out from a block (i.e., a cluster) including the physical address 110h at which the data should start to be written. In this example, the read operation is supposed to have failed and this block is treated as a defective block.
In Step (2), a portion of the data that has been read in Step (1) is replaced with the requested data at the location specified, thereby newly generating one block of data.
In Step (3), a block in the spare area 15 (with a top physical address 10000h, for example) is assigned as a replacement block to the defective block, from which data has been read in Step (1), and the one block of data, which has been generated in Step (2), is written in that replacement block.
Although the user has requested only the write processing step, the RMW processing includes a data read operation (which will be referred to herein as a “read processing step”) and a data write operation (which will be referred to herein as a “write processing step”). Before the write processing step is carried out, the read processing step may fail for some reason (e.g., due to deposition of dust on the surface of the disk) and data may be unable to be read from that block properly. However, since the user has requested writing, it is not preferable to regard it as a write error because reading has failed.
As for a BD, it was proposed that flag information called “flag bits”, indicating the status of the block or sector, be included in the BIS data and that two-bit information called “status bits (Sa)”, indicating the status of data on a sector-by-sector basis, be included in that flag information (see Patent Document No. 3, for example). The status bits of the sector, at which reading has failed during the RMW processing, are changed into a value indicating the failure (e.g., a binary number “10”). According to Patent Document No. 3, the status bits are actually supposed to be “01”. However, the bits are supposed herein to be “10” for convenience sake.
The data of a sector, of which the status bits are currently “10”, will be referred to herein as “data in discard state”. Likewise, a block including such data in the discard state will be referred to herein as “block in discard state”. In other words, the “block in discard state” means a block, of which the block data needs to be (or can be) complemented with data of another block at least partially.
However, even if such status bits are added to the sector, data still remains stored in the replacement block with the data that has not been read successfully still missing.
Meanwhile, it is true that the original block, at which the read operation failed during the RMW processing, was soiled with dust, finger marks or anything like that. However, the user may already have wiped the soil or dust off and the data in question may be readable properly when reading is tried next time. For that reason, it was proposed that another piece of information called “previous location address” (which will be abbreviated herein as “PLA”) be included in the flag bits on a BD (see Patent Document No. 3, for example).
This PLA is information that is valid only within the replacement block, and is physical address information showing at what physical address location the data in the replacement block with this PLA has been stored previously. In a BD-RE, PLA with a valid value is set only in the replacement block in the spare area 15a or 15b and zero representing null state is always set in any other block in the remaining area (i.e., the user data block 14).
When Data A is read from the replacement block in the discard state, Data B identified by PLA is also read from the defective block. And if Data B has been read successfully, Data A is complemented with that Data B. In this manner, the original data can be restored properly. That is why PLA is significant valid information for the replacement block in the discard state.
Hereinafter, the RMW processing will be described in further detail with reference to FIG. 6A and FIG. 6A, in which FIG. 6A shows the types of status bits and FIG. 6B shows the RMW processing.
As shown in FIG. 6B, if read operation has failed during the PMW processing, then the PMW processing is carried out by performing:                Step (1) of generating dummy data in which the status bits of all sectors within a block are set to be “10” according to the binary notation;        Step (2) of modifying the data that has been generated in Step (1) with the data to be written and changing the status bits of the modified sectors into “00” according to the binary notation; and        Step (3) of writing the data that has been generated in Step (2) in the replacement block.        
Hereinafter, the correlation between the PLA and the defect entries 23 will be described with reference to FIG. 7 A and FIG. 7B. In FIG. 7A and FIG. 7B, the physical addresses that should be assigned to sectors are supposed to be assigned to blocks 3 for the sake of simplicity.
FIG. 7A shows the status of the disk yet to be subjected to the RMW processing. As shown in FIG. 7A, if a request to write data, of which the size is smaller than one block unit, on a block with physical address D has been submitted, the RMW processing needs to be carried out. However, this block with the physical address D is supposed to be defective and data cannot be read from the block properly.
FIG. 7B shows the status of the disk that has been subjected to the RMW processing. Since data cannot be read from the block with the physical address D properly, the status bits thereof are changed into “10” according to the binary notation, and the data to be written is modified and written on a replacement block with physical address A in the spare area 15.
In this case, the PLA value of the block with the physical address A is defined so as to refer to the physical address D. Also, since an alternative write operation has been performed due to the presence of a defect, a defect entry 23 with entry attribute RAD0, of which the defect location information 31 is physical address D, the replacement's location information 33 is physical address A and the sub-attribute 32 is discard state (represented by a binary number “1000”), is added to the defect list 21 (see FIG. 3).
FIG. 8A and FIG. 8B show how to perform complementing processing on data in the discard state. Specifically, FIG. 8A shows a replacement block with physical address A and in the discard state, of which the PLA value is defined so as to indicate physical address D. FIG. 8B shows the procedure of the complementing processing. As shown in FIG. 8B, if all data has been read properly from the original block with physical address D, then the data that has been read from the replacement block is complemented with the data of the original block, thereby restoring the original data correctly.
Meanwhile, if data cannot be read properly from the block identified by the PLA in response to a read request, then the read request will result in an error.
FIG. 9 is a flowchart showing the procedure of so-called “PLA tracing” processing to complement data. Hereinafter, the respective processing steps will be described as being applied to the example shown in FIG. 8.
The first step 801 is moving to the replacement block to read data from. In this example, the optical head is moved to the location with physical address A shown in FIG. 8.
The next step 802 is reading data from the target replacement block.
The third step 803 is determining whether the read data is in the discard state or not (whether the PLA is effective or not). More specifically, it is determined whether or not the read data includes status bits “10”.
If the answer is YES, then the next step 804 is moving to the original block identified by the PLA. For example, the optical head is moved to the location with the physical address D shown in FIG. 8.
The next step 805 is reading data from the target original block and complementing the data that has been read from the replacement block with the former data.
If the data that has been generated in Step 805 is still in the discard state, the series of processing steps 803 through 805 are repeatedly performed a number of times. Optionally, this repetition processing step may be omitted.
The final processing step 806 is determining the data to be definitive one if the data has turned out to be no longer in the discard state.
Next, blocks to be certified will be described. In a BD-RE, blocks, which are checked with ◯ in its target of certification column of the entry attribute in FIG. 4B, are designated as a target of certification. Only the block with the SPR attribute, of which the sub-attribute 32 does not include the “RDE” information, is not the target of certification. More specifically, the blocks to be certified are listed as defect entries 23 in the following five entry attributes 30:                A block designated by the defect location information 31 of a defect entry 23, of which the entry attribute 30 is RAD;        A block designated by the defect location information 31 of a defect entry 23, of which the entry attribute 30 is NRD;        A block designated by the replacement's location information 33 of a defect entry 23, of which the entry attribute 30 is SPR (and of which the sub-attribute 32 must include “RDE” information);        An area that starts with a block designated by the defect location information 31 of a defect entry 23, of which the entry attribute 30 is PBA, and that includes a number of continuous blocks designated by the replacement's location information 33; and        A block designated by the replacement's location information 33 of a defect entry 23, of which the entry attribute 30 is UNUSE.        
In the quick-certify processing, the defect list 21 is subjected to the following processing based on the results of the certification:
(1) Block that couldn't be certified successfully                If a block, of which the entry attribute 30 is SPR (i.e., of which the sub-attribute 32 includes “RDE”), could not be certified successfully, then the defect entries are changed into a defect entry 23 with the UNUSE attribute, of which the replacement's location information 33 designates that block.        If a block, of which the entry attribute 30 is PBA, could not be certified successfully, then a defect entry 23 with the RAD or NRD attribute, of which the defect location information 31 designates that block, is added and the defect entry 23 with the PBA attribute is deleted.        
(2) Block that could be certified successfully                If a block, of which the entry attribute 30 is RAD or NRD, could be certified successfully, then a defect entry 23, of which the defect location information 31 designates that block, is deleted.        If a block, of which the entry attribute 30 is PBA, could be certified successfully, then a defect entry 23, of which the defect location information 31 designates that block, is deleted.        If a block, of which the entry attribute 30 is SPR (and of which the sub-information 32 includes RDE information), could be certified successfully, then defect entries are changed into a defect entry 23 with the SPR attribute, of which the sub-information 32 does not include the RDE information.        If a block, of which the entry attribute 30 is UNUSE, could be certified successfully, then defect entries are changed into a defect entry 23 with the SPR attribute, of which the sub-information 32 does not include the RDE information.        
Patent Document No. 1: Japanese Patent Application Laid-Open Publication No. 2000-222831
Patent Document No. 2: Japanese Patent Application Laid-Open Publication No. 2004-253109
Patent Document No. 3: United States Patent Application Publication Ser. No. 2006/0077816
Non-Patent Document No. 1: Information Technology—Multi-Medium Command-5 (MMC-5), [online], [searched the Internet on Jun. 28, 2006], the Worldwide Web URL: http://www.t10.org/ftp/t10/drafts/mmc5/mmc5r03.pdf.
In the quick-certify processing, only the defective block on the defect list 21 (see FIG. 3) is subjected to the certification processing. And depending on the results of the certification processing, the defect entries 23 are deleted, changed or added as described above. However, if a block with the RAD or NRD attribute could not be certified successfully, for example, there would be some problems. For instance, if such a block could not be certified successfully, the defect entry 23 with the RAD attribute could be left as it is or the attributes could be changed into RAD by assigning a replacement block to the block that has turned out to be defective.
There are two types of RAD attributes, namely, RAD0 and RAD1 attributes. The difference between these two attributes is whether the data of the replacement block is valid or not, i.e., whether the data should be read from the replacement block or the original block. Supposing a block that has caused an error as a result of the certification processing is listed as a block with the RAD1 attribute, if an RMW request on that block were submitted, then read processing should be performed on a defective block. In that case, the data would most probably be unreadable and the read processing would have to be retried, thus deteriorating the processing performance, which is a problem. A similar problem would arise even if a block that has caused an error as a result of the certification processing were listed as a defect entry 23 with the NRD attribute.
It should be noted that since the defect entry 23 with the PBA attribute is defined to be no longer existent after the quick-certify processing, no block could be listed as a defect entry 23 with the PBA attribute.
That is why a block that has caused an error as a result of the certification processing is preferably listed as a defect entry 23 with the RAD0 attribute. In a block with the RAD0 attribute, the replacement block would be accessed no matter whether the request submitted is a read request or a write request. In the quick-certify processing, certification is done on only a defective block but nothing particular is carried out on a spare area being used as an alternative area. For that reason, if there is a replacement block in the discard state, information showing the discard state will remain as it is in the replacement block even after having been subjected to the quick-certify processing. Meanwhile, in cases of full-certify processing, the entire data area 5, including the spare areas 15a and 15b, is all subjected to the certification processing, and therefore, no block in the spare area could remain in the discard state.
In a situation where that piece of information showing the discard state remains as it is in the replacement block even after the defective block has been subjected to the quick-certify processing, if a request to perform a read operation (specifically, read operation of RMW processing) on that replacement block is submitted next, then the PLA tracing processing shown in FIG. 9 needs to be carried out. Since there is no valid user data in the original block identified by the PLA as a result of the quick-certify processing, this PLA tracing processing is not only meaningless but also would deteriorate the performance.
Another problem will be described. In the defect list 21, stored are the defect entries 23 that have been sorted in the ascending order by their eight-byte values (more exactly, their 63-bit values except the most significant bits). That is to say, the physical addresses of the defective blocks are stored after those blocks have been grouped according to their entry attributes 30. But the defective blocks are not stored in the order of physical addresses.
Specifically, if there are four physical addresses A, B, C and D (where A<B<C<D), B and D are listed as defect entries 23 with the RAD0 attribute on the defect list 21, and A and C are listed as defect entries 23 with the NRD attribute on the defect list 21, then defect entries 23 with the following combinations of attributes and physical addresses:
RAD0B,RAD0D,NRDA, andNRDCare stored in this order in the defect list 21.
Suppose the optical disk medium 1 has only one storage layer and defective blocks are going to be subjected to the quick-certify processing sequentially in the order that is defined in the defect list 21. In that case, first, quick-certify processing is performed on a defective block with the RAD0 attribute with the optical head moved from the inner area of the disk toward the outer area thereof. After that, the optical head goes back to the inner area of the disk to perform quick-certify processing on a defective block with the NRD attribute, and then heads back toward the outer area again. As there are five types of entry attributes 30, the optical head may sometimes have to move from the inner area toward the outer area five times. Even if the optical disk medium 1 has a number of storage layers, the optical head also has to go back and forth between multiple areas in the order of physical addresses. As a result, it would take a lot of time to get the quick-certify processing done.